The present invention relates to a rotating electric machine such as a turbine generator having its rotor provided with a ventilation mechanism which directly cools the rotor with cooling fluid.
In general, a mechanism is well known wherein ventilation ducts are provided in the stator or the rotor of a rotating electric machine such as a turbine generator, and cooling fluid such as air or hydrogen gas is passes through the ventilation ducts so that the coils and the iron cores heated up due to the generated joule loss and iron loss are cooled down.
From the viewpoint of achieving a high cooling performance, a direct cooling system which cools the coils by putting them in direct contact with cooling fluid is widely employed as a mechanism for cooling the rotor. Recent requirements have been for the compatibility of the scale-up of the rotating electric machines and the reduction in the costs of such high capacity machines. The high capacity requirements tend to increase the length of the rotor in the direction along the rotor shaft of the rotating electric machine.
A typical structure of the conventional ventilation mechanism for use in a rotating electric machine will now be described in reference to FIGS. 16˜19.
FIG. 16 schematically shows in vertical cross section a part of a turbine generator having the rotor provided with a radial flow cooling system. In FIG. 16 are shown a turbine generator 1, a stator 2, a rotor 3 and a rotor shaft 4.
An axial fan 5 installed near one end of the rotor shaft 4 generates the flow of cooling fluid 6 (depicted with arrows) passing through the various ventilation ducts in the rotating electric machine. Sub slots 7 to serve as ventilation ducts for conducting the cooling fluid 6 through the rotor 3 are provided underneath the coil slots of the rotor 3, running along the rotor shaft 4. Rotor field coil (of electric conductor) 8 of laminated structure are fitted in the coil slots formed above the sub slots 7. Radial ducts (holes: radial cooling fluid ducts) 9 for guiding the cooling fluid from the sub slots 7 into the laminated field coils 8 are cut in the laminated field coils 8 in the radial direction of the rotor 3. The radial ducts 9 are juxtaposed at a predetermined interval in the axial direction of the rotor and the discharging holes 10 of the radial ducts 9 are also juxtaposed on the outer circumferential surface of the rotor 3 in the axial direction of the rotor 3.
An air gap 11 is defined between the inner circumferential surface of the stator 2 and the outer circumferential surface of the rotor 3.
The iron core 12 of the stator 2 is provided with stator cooling ducts (cooling fluid ducts) 13 which are juxtaposed in the axial direction of the rotor shaft 4 and serve as radial ventilation ducts (holes) for guiding the cooling fluid 6 through the stator 2. Reference numeral 14 indicates the stator coil of electric conductor fitted in the stator coil slots, and numeral 15 denotes a cooler for cooling down the cooling fluid 6 whose temperature is elevated as a result of cooling the parts of the turbine generator 1.
The constituent elements (before lamination) of the field coils 8 are flat plates (not shown) of electric conductor and each element has ventilation holes arranged in the axial direction. A plurality of such elements are stacked (laminated) one upon another in the radial direction in such a manner that the ventilation holes are registered one upon another to form plural juxtaposed radial ducts 9 arranged in the axial direction of the field coils 8.
These plural radial ducts 9 are communicated with the sub slots 7 provided at the bottom of the field coil 8. When the rotor 3 starts rotating, the cooling fluid 6 flows into the sub slots 7 due to the pumping action caused by the pushing force of axial fan 5 and the centrifugal force created in the radial ducts 9. Part of cooling fluid 6 forced out by the axial fan 5 flows toward the air gap 11 and the far end of the stator coil 14. Part of the cooling fluid 6 entering the sub slots 7 is distributed into the respective radial ducts 9 while flowing from the central position of the rotor shaft 3 toward the far end thereof. Then, the cooling fluid 6 cools the field coils 8 while it is flowing through the radial ducts 9, and the cooling fluid 6 is discharged from the outlet holes 10 of the radial ducts 9 into the air gap 11. Thereafter, the cooling fluid 6 flows from the air gap 11 into stator cooling ducts 13, cools the iron core 12 and the stator coil 14, and joins that part of the cooling fluid 6 which has cooled the end of the stator coil 14. Next, the confluent cooling fluid 6 whose temperature is elevated as a result of having cooled the heat generating parts, flows into the cooler 15 for lowering the temperature of the cooling fluid 6. The thus cooled fluid 6 finally returns to the axial fan 5 to complete the whole circulation.
The rotors of radial flow cooling type are disclosed in, for example, JP-A-09-285025, JP-A-2005-210893 and JP-A-10-178754.
The rotors of radial flow cooling type are advantageous in that both facility in fabrication of the rotor 3 and reduction in production cost can be attained since plural radial ducts 9 can be formed in the field coils 8 simply by stacking (laminating) flat conductors of the same structure in the radial direction. On the other hand, since the cooling of the field coil 8 is performed by distributing the cooling fluid 6 flowing through the sub slots 7 into the respective radial ducts 9 in the order of increasing distance from the axial fan 5, the rate of flow of the cooling fluid 6 decreases with the distance from the axial fan 5 due to the increase in the flow resistance as the distance from the axial fan 5 increases. This situation gives rise to a problem that the temperature of the field coil 8 becomes higher near the central part thereof. Therefore, this problem has made it difficult to increase the axial length of the rotor 3 for higher capacity. Thus, the rotors of radial flow cooling type have been applied to relatively small capacity machines having ratings of up to 100 MVA.
There is another type of rotor, i.e. rotor of gap pick up diagonal flow cooling type, known in, for example, JP-A-2000-139050.
FIG. 17 schematically shows in partial cross section of a turbine generator having a rotor of gap pick up diagonal flow cooling type.
The laminated field coil 8 of the rotor 3 has V-shaped diagonal ducts 16 cut therein, and the holes 17 of the diagonal ducts 16 are formed in the outer surface of the rotor 3. A main cooler 18 serves to cool down the cooling fluid 6 whose temperature is elevated as a result of having cooled parts of the turbine generator, and a sub cooler 19 is provided for the same purpose.
In the stator 2 are provided stator cooling ducts 13 in juxtaposition in the axial direction of the turbine generator.
According to this type of rotor as described above, there are defined the reverse zone 20 where the cooling fluid 6 flows through the stator cooling ducts 13 inwardly in the radial direction and the forward zone 21 where the cooling fluid 6 flows through the stator cooling ducts 13 outwardly in the radial direction.
The field coil 8 is made up of plural flat shaped conductors (not shown) stacked (laminated) one upon another, each having plural ventilation holes arranged in the axial direction, and the communicated ventilation holes make up the diagonal ducts 16 in the field coil 8. Further, ventilation holes are cut in each flat conductor in two rows arranged in the circumferential direction (i.e. direction parallel to the sheet of the drawing) so that the V-shaped diagonal ducts 16 in the field coil 8 are configured in a net shape.
The cooling fluid 6 forced out by the axial fan 5 first cools the end of the stator coil 14 and then flows into the sub cooler 19, where the temperature of the cooling fluid 6 is lowered. The chilled cooling fluid 6 out of the sub cooler 19 flows into the stator cooling ducts 13 in the reverse zone 20 to cool the iron core 12 and the stator coil 14, and is discharged into the air gap 11. Then, the cooling fluid 6 is conducted through the suction holes (holes) 17 into the diagonal ducts 16 and passes through the diagonal ducts 16 inwardly in the slanted direction to cool the field coil 8. Thereafter, the cooling fluid 6 changes its flow direction at the bottom of the field coil 8, flows outwardly in the slanted direction to cool the field coil 8 again, and is discharged at the discharge holes (holes) 10 into the air gap 11.
The cooling fluid 6 now flows from the air gap 11 into the stator cooling ducts 13 in the forward zone 21, cools the iron core 12 and the stator coil 14, and flows into the main cooler 18. The temperature of the cooling fluid 6 is lowered in the main cooler 18, and the chilled cooling fluid 6 returns to the axial fan 5 to complete the whole circulation.
The mechanism of the gap pick up diagonal flow cooling will here be described in reference to FIGS. 18A, 18B and 19.
FIG. 18A shows the structure of the suction hole provided in the rotor cooling duct 9, and FIG. 18B shows the structure of the discharge hole provided in the rotor cooling duct 9.
A cut 28 is formed in the suction hole 17 of the rotor cooling duct 9, and a projection 29 is formed downstream of the discharge hole 10 of the rotor cooling duct 9. Reference numeral 31 indicates a region for raising pressure defined in the suction hole 17, and numeral 32 denotes a region for lowering pressure defined behind the projection 29 at the discharge hole 10.
When the rotor 3 starts rotation, the circumferential flow of cooling fluid 6 is generated in the air gap 11. Since the cuts 28 are formed in the suction holes 17 in the circumferential direction, part of the cooling fluid 6 near the circumference of the rotor 3 is conducted in such a direction as to cause the fluid to collide with the inner walls of the suction holes 17. As the fluid approaches the inner walls, the static pressure of the fluid recovers with the result that the higher pressure regions 31 are formed in the suction holes 17. The symbol hi indicates the depth of the cut 28 of the suction hole 17.
On the other hand, since the projections 29 are formed downstream of the discharge holes 10, the circumferential flow of the cooling fluid 6 creates separation vortices behind the projections 29. As a result, the low pressure regions 32 are formed in the discharge holes 10. The symbol ho denotes the height of the projection 29.
The flow rate of the cooling fluid 6 flowing through the diagonal duct 16 in the rotor depends on the difference between the pressure in the higher pressure region and the pressure in the low pressure region. FIG. 19 shows in graphical representation the relationship between the flow rate Q and the pressure rise P. In FIG. 19, solid curve represents the Q-P characteristic which is similar to that applicable to a pump or a fan, and broken curve gives the pressure loss characteristic of the cooling fluid 6 distributed from the suction hole 17 to the discharge hole 10. The intersection between the Q-P characteristic curve and the pressure loss characteristic curve defines the operating point which determines the flow rate of the cooling fluid 6 through the diagonal duct 16.
In the structure of the rotor having the gap pick up diagonal flow cooling system, the flow rate of the cooling fluid 6 for cooling the field coil 8 is securely maintained by providing plural pairs of suction hole and discharge hole in the circumferential surface of the rotor 3 and forming the diagonal duct 16 between each pair of the suction hole and the discharge hole. This constitution allows the repetition of the unit structures each having the diagonal ducts 16, in the axial direction of the rotor shaft so that uniform cooling performance can be expected in the field coil 8 in the axial direction, which is advantageous in that the axial elongation of the rotor 3 and therefore the scale-up of the capacity of the turbine generator can be realized. On the other hand, the complexity in the employed shape of the cooling fluid ducts results in an increase in production man-hour of the rotor 3 and makes the reduction in cost difficult. Accordingly, this constitution is used only for large capacity machines having ratings of higher than 500 MVA.